My one-man band, SkyValve, does a combination of Prog/thrash/death metal. Sorta like Sylosis, Testament, Ayreon, and Dethklok rolled into one. I do vocals and rhythm guitar (can't play lead...use keys/synths for leads, which you don't see thrash use often .)

Do you have any suggestion on recording or songwriting? When I write, I generally focus on chromatic/Maiden like riffs with some synth athmosphere. Oh, and use of both death growls and shouting for vocals.

Try writing on world events, or an experience you've been through. I've only wrote ballads and rap, but you can still apply it to the genres you play. Listen to Slipknot, Escape the Fate, Bring Me The Horizon and stuff like that. This next one might be more towards rock, but try War Pigs - Black Sabbath. They wrote it about war and politics. People thought the song was Satanic because of the final bar;

"Now in darkness world stops turning
Ashes where the bodies burning
No more war pigs have the power
Hand of God has struck the hour
Day of judgement, God is calling
On their knees the war pig's crawling
Begging mercy for their sins
Satan laughing spreads his wings
Oh lord yeah!"

But besides that, try it. See how the songwriting goes.

Now on recording, or screaming altogether, try not to over-do it. You'll destroy your vocal chord. Drink a lot of water or something. I can't scream or growl (I have tried), but I do know people who do. One mentioned that it will destroy your vocal chord. I'm just saying drink water as a recommendation. Look after your voice man.

To TomB-guitarist:
I'll take your advice on the vocals and lyrics (love talking about evil, metaphorical stuff! )
To Hail:
I honestly don't really know many musicians where I live...
To Celitus:
I actually know many writing techniques, tempos/time signatures, and styles of writing (i've written to many riffs and completed songs to count! ), it's just that I need additional feedback...I'm still learning.

And on the other hand, i have an idea for a song in 9/8 that plays like it is 3/4...kind of a polyrhythm thing. Just an idea...I may get to recording later...

I know the feeling. I rarely have time, and usually when I do I don't work on what I should work on, but either dick around like a lazy ass, practice more of the same stuff within my comfort zone (ear training, rhythm, reading, or whatever song I am working on for classical lessons) and only every once in a while work on my electric guitar chops or recording (focusing on drum programming atm)... At least I know next weekend I'll be completely free and will just focus on figuring out drums for a couple of tracks I want to record.

Just make sure you dont fall into the trap that I see most thrash bands have these days where they label themselves as "prog" to try and stand out, when really what they are saying is "we try to write more complicated riffs than metallica"

I see what you mean. I try not to be overly complicated. I stick to like 2-4 concepts with a song, and evolve them throughout not just the song, but other songs, like concept albums (which I love!). Like Coheed and Cambria or Protest the Hero (two of my favs, although not extreme metal...)
On the other hand...stay tuned...recording has commenced!

Huh. Usually I just write whatever's in my head. Or I just mess with my keyboard until I have something.
Probaly should mention that I also love j-pop/metal (Blood Stain Child, Dir En Grey, Vocaloids (no, I'm seroius))
Oh, and ANYTHING Sweedish.